Method and apparatus for measuring temperature

ABSTRACT

Temperature of molten silicon  1  in an infrared image furnace  2  including a halogen lamp  8  as a heating source to grow a single crystal of silicon in a floating-zone method is measured with high precision according to light radiated from the molten silicon  1 . By disposing an optical path tube extending to the molten silicon  1 , light propagating from the molten silicon  1  in a particular direction can be extracted. As a result, light radiated from the molten silicon  1  can be extracted while reducing the influence of disturbance of light from various directions such as light radiated from the halogen lamp  8 , reflected light and scattered light thereof, and the like. Luminance of light thus extracted is measured by a CCD camera  7  to obtain the temperature according to the luminance, and hence the temperature can be measured with high precision using a measuring apparatus of a simple configuration.

TECHNICAL FIELD

The present invention relates to a non-contact type temperaturemeasuring apparatus used for forming a semiconductor device usingradiant heating from a heating source with high luminance such as aninfrared halogen lamp, especially employed in a device to form a crystalsuch as single-crystalline silicon and single-crystal oxides using afloating zone method (FZ), an infrared annealing furnace for asemiconductor substrate, an infrared epitaxial furnace, and the like.

RELATED ART

Today, single-crystalline silicon used as a substrate material of apower device or the like is manufactured primarily using the zonefloating (FZ) method. This is a method in which a rod of polycrystallinesilicon as a source material is locally melted to form a floating zoneand single-crystalline silicon is manufactured using a property thatmolten silicon in the floating zone forms a single crystal following ona seed crystal. In the FZ method, the molten silicon is held by surfacetension and the like to form a floating zone. Therefore, from whensilicon is melted to molten silicon to when the single crystal is formedas a solid state, the molten silicon is not brought into contact withany members such as a container excepting ambient gas in the furnace. Inconsequence, when compared with a Czochralski method (CZ method) or thelike in which silicon is melted in a container such as a quartzcrucible, the FZ method is advantageous in that the single-crystalsilicon can be manufactured with higher purity.

For the FZ method, to increase quality of the single crystalline siliconby managing and controlling growth thereof with high precision, therehas been required a method of correctly measuring surface temperature ofsilicon in the floating zone in a non-contact method.

Problem to be Solved by the Invention

However, for the measurement of the surface temperature of moltensilicon (melting point is 1420° C.) as a high-temperature liquid, atechnique to measure temperature in a non-contact method in which thetemperature is measured by sensing light radiated from the surface hasnot been fully established. This is because the molten silicon has ahigh reflection factor. In other words, when it is desired to measurelight radiated from a surface of molten silicon in the floating zone inthe FZ method, high-luminance light radiated from a high-frequency lightsource such as a heating coil in an FZ furnace reflected on a surfacewall formed in a state of a mirror surface to form a reflection imageand the image is again reflected on the surface of molten silicon in thefloating zone, and the reflected light becomes a disturbance against theoriginal, radiated light corresponding to the temperature of the moltensilicon, which makes it difficult to sense the information of thetemperature.

Therefore, conventionally, as a method of measuring the temperature ofmolten silicon in the floating zone in the FZ furnace, there has beenadopted an indirect temperature measuring method in which a thermocouplesealed in a quartz tube is brought into contact with a heat source tomeasure the temperature to estimate the temperature of molten siliconaccording to results of the measurement. In such an indirect measuringmethod, it is difficult to correctly measure the temperature in thesilicon floating zone.

Moreover, as a method to measure temperature of a single crystal grownin the CZ method, Japanese Patent Laid-Open Publication No. SHO59-227797 proposes a method to measure in a CZ furnace, heatertemperature, molten-crystal temperature, and boundary temperaturebetween a molten crystal and a crystal using a thermocouple to measure agradient of the temperature in the crystal according to the results ofthe measurement. However, it is difficult to apply this method to the FZmethod, and there is a fear that the purity of single-crystal silicon islowered by using the thermocouple.

There has been known an event associated with the CZ method, that is,when the single crystal is grown by drawing the single crystal upwardfrom molten silicon, there appears a ring-shaped high-luminance zonearound the growing section of the single crystal. To increase yield ofthe products, there have been proposed the methods to measure a crystalgrowing state, utilizing this phenomenon, which are a method to byobtaining the high-luminance zone by a charge-coupled device (CCD)camera using the event such as a method to measure a diameter of thecrystal (Japanese Patent Laid-Open Publication No. SHO 63-100097), amethod to measure width of deflection of the crystal (Japanese PatentLaid-Open Publication No. SHO 63-170296), a method to measure height ofsurface of molten crystal (Japanese Patent Laid-Open Publication No. HEI2-102187), and a method to measure vibration of surface of moltencrystal (Japanese Patent Laid-Open Publication No. HEI 4-12233).

Also in the CZ method, to measure the temperature by sensing, by a CCDcamera or the like as above, light radiated from a surface, the lightradiated from the heater to melt silicon becomes disturbance. Therefore,it is required to carry out complicated correction and hence it isdifficult to correctly measure the temperature. To cope with thisdifficulty, Japanese Patent Laid-Open Publication No. HEI 10-142063proposes a method in which the influence of the disturbance of the lightis removed by simple correction using the event of occurrence of thering-shaped high-luminance zone as described above. However, this methoduses the above-mentioned event unique to the CZ method and hence cannotbe applied to the FZ method.

It is therefore an object of the present invention to provide anon-contact temperature measuring apparatus to measure temperature of asurface of a substance by sensing, with a CCD camera or the like, thelight radiated from the surface of the substance, the apparatus beingalso capable of measuring temperature of molten silicon in the FZ methodwith high precision.

DISCLOSURE OF THE INVENTION

To achieve the above object according to the present invention, there isprovided a non-contact type temperature measuring apparatus to measurethe temperature of a heated substance in a furnace including ahigh-luminance light source from the luminance obtained by measuringlight radiated from the heated substance, characterized by comprising awindow section to transmit light from the furnace to an external space,an optical path tube extending from the window section to the heatedsubstance, and an image receiver to measure light introduced from theheated substance via the optical path tube and the window section.

According to the configuration, by using an optical path tube, it ispossible to extract the light radiated from the heated substance,propagating in a particular direction. It is therefore possible that theinfluence of the disturbance of light from various directions such aslight radiated from the high-luminance light source, reflected lightthereof, and scattered light thereof can be lowered to extract lightradiated from the heated light to thereby measure temperature with highprecision.

In the temperature measuring apparatus according to the presentinvention, the temperature can be appropriately measured in the furnaceof the floating-zone method of the prior art in which a material ismelted by a high-luminance light source as a heat source to generate afloating zone to grow a crystal and in which the temperature cannot beeasily measured in a non-contact method. Moreover, the temperature ofmolten silicon for which the disturbance of the light easily occursbecause of its high reflection factor can be appropriately measured.

As a material of the optical path tube, carbon is preferably usedbecause carbon is highly resistive against high temperature and has ahigh light absorption factor and it is possible to suppress theoccurrence of the scattered light as the disturbing light in the opticalpath tube. As the image receiver, a CCD camera capable of measuringluminance with high precision can be suitably employed.

In the image receiver, it is favorable to dispose a wavelength cutfilter to interrupt a light in a range of wavelengths corresponding tothose of light radiated from the high-luminance light source. Byarranging the wavelength cut filter, the influence of reflected light ofthe light radiated from the high-luminance light source can beefficiently reduced. In addition, a band-pass filter to extract thelight in a range of wavelengths corresponding to those of the light forwhich the image receiver has high sensitivity is desirably disposed inthe image receiver. By arranging the band-pass filter, the influence ofdisturbing the light with various wavelengths caused by scattering andthe like of the reflected light of the light radiated from thehigh-luminance light source can be efficiently minimized.

As a material of the window section, quartz can be used. If sapphire isadopted as the material of the window section, the temperature can bemeasured with higher precision because sapphire is a substance having arelatively high value of transmittance for light in an infrared rangeused for the temperature measurement.

According to the present invention, there is provided a temperaturemeasuring method of measuring temperature of a heated substance in afurnace including a high-luminance optical source as a heating source,characterized by comprising

a step of introducing light from the heated substance via an opticalpath tube extending to the heated substance, a step of measuringluminance of the light introduced via the optical path tube, and a stepof calculating temperature of the heated substance according to theluminance.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram showing a temperature measuring apparatusin an embodiment of the present invention.

FIG. 2 is a schematic diagram showing an apparatus in which athermocouple is disposed to the apparatus of FIG. 1 for experiments.

FIG. 3 is a graph showing results of temperature measurements by thetemperature measuring apparatus of FIG. 2.

FIG. 4 is a graph showing a Fourier spectrum of the graph of FIG. 3according to results of temperature measurement by a CCD camera.

FIG. 5 is a graph showing a Fourier spectrum of the graph of FIG. 3according to results of temperature measurement by a thermocouple.

BEST MODE FOR CARRYING OUT THE INVENTION

Next, an embodiment of the present invention will be described byreferring to the drawings.

FIG. 1 shows a schematic diagram of a non-contact temperature measuringapparatus of the embodiment in which the present invention is applied toan infrared image furnace 2 to manufacture single-crystal silicon in theFZ method.

First, description will be given of a configuration of the infraredimage furnace 2 to manufacture single-crystalline silicon.

In the infrared image furnace 2, a halogen lamp 8 is disposed as aheating light source and a silicon raw material rod 15 is set. Thefurnace 2 has an inner surface formed as a mirror surface by platinggold such that the light radiated from the halogen lamp 8 is reflectedon the surface to be concentrated onto a particular area of the materialrod 15. In this way, by concentrating the heating light onto theparticular area of the rod 15, a temperature gradient occurs in the rawrod 15, and the particular area of the rod 15 is melted to moltensilicon 1 to thereby generate a floating zone.

A single crystal of silicon is manufactured in the FZ method in whichthe floating zone is first generated in the vicinity of a seed crystaland the floating zone is moved to sequentially grow a single crystalbeginning at the seed crystal. FIG. 1 does not show details of amechanism to move the rod 15, a mechanism to regulate ambient gas in thefurnace, and the like necessary for the manufacturing.

Incidentally, silicon has a melting point of about 1420° C., and as thehalogen lamp 8 to heat the rod 1, a lamp resistive against temperatureup to about 3000° C. is used.

Next, description will be given of a configuration of a temperaturemeasuring apparatus according to the present invention.

In the infrared image furnace 2, a window section 13 is disposed on awall to pass light therethrough, the wall being on a side of a heatinglight concentration area, namely, of a section in which molten silicon 1is generated. In the furnace 2, an optical path tube 3 is disposed toextend from the window section 13 to an area in which the molten silicon1 is generated. Outside the furnace 2, there is disposed a CCD camera 7to sense the light which is radiated from the molten silicon 1 and whichis introduced via the optical path tube 3 and the window section 13 suchthat the attitude of the camera 7 is adjusted by a camera holder 14. Inthe CCD camera 7, there is mounted an optical lens 6 including awavelength cut filter 4 to interrupt the light in a particular range ofwavelengths and a band-pass filter 5 to extract the light in aparticular range of wavelengths. The CCD camera 7 is connected to animage processor 9 to extract a variation in luminance from the CCDcamera's output signal to output the variation therefrom. The imageprocessor 9 is connected to a computer 10 which accumulates its outputsignal from the processor 9 to analyze the signal.

As described above, heretofore, when it is desired that the lightradiated from the molten silicon 1 is measured to obtain the temperatureof the molten silicon 1 through the measurement in the prior art, thelight radiated from the halogen lamp 8 as a heat source and thereflected and scattered light thereof become disturbance, and the lightcannot be correctly measured and hence it is difficult to obtain thetemperature of the molten silicon 1. In this situation, the presentinventor considered that by obtaining the light radiated from the moltensilicon in a particular direction by use of the optical path tube 3, thelight radiated from the molten silicon 1 can be extracted while loweringthe influence of disturbing light coming from various directions. Thetemperature measuring apparatus according to the present invention ischaracterized in that such an optical path tube 3 is disposed therein.

Moreover, the light radiated from the halogen lamp 8 has a wavelength upto about 15 micrometers (μm) with a peak of about one micrometer.Therefore, to reduce the influence of the light, a wavelength cut filter4 is employed to interrupt the light of a long wavelength ranging fromabout 1.0 μm to about 15.0 μm, namely, from a near-infrared light to afar-infrared light.

Additionally, a camera including an Si-CCD as a sensor element (768×492pixels) having a sensing characteristic to sense light with a wavelengthranging from about 0.4 μm to about 1.1 μm is used as the CCD camera 7.In association with the sensing characteristic, a band-pass filter 5having a maximum point of transmittance of about 0.83 μm to transmittherethrough light with a wavelength ranging from about 0.7 μm to about1.1 μm is disposed. That is, the radiated light in a wavelength zoneranging from about 0.7 μm to about 1.0 μm is used to measuretemperature. In this way, by limiting the wavelength range for themeasurement to cut the light beyond the wavelength, it is possible toreduce the influence of the disturbance of light with variouswavelengths caused by scattering on a surface of the molten silicon 1 orthe like.

The optical path tube 3 is used in the vicinity of the molten silicon 1at a temperature of about 1420° C. and is hence favorably made of amaterial resistive against temperature equal to or more than thistemperature. Furthermore, to prevent an event in which light fromvarious directions such as scattered light resultant from scattering ofthe light radiated from the halogen lamp 8 on a surface of the moltensilicon 1 is reflected in the optical path tube 3 and reaches the CCDcamera 7 to cause the disturbance in a sensed image, the tube 3 isfavorably made of a material which does not easily reflect light.Therefore, in the present invention, carbon is used as the material ofthe tube 3 because carbon is resistive against temperature up to about1500° C. and has a relatively high absorption of light. Alternatively,SiC or the like may also be used.

In the embodiment, the optical path tube 3 has a diameter of about 10millimeters (mm). However, to set the temperature distribution in theinfrared image furnace 2 to a possibly uniform state, it is desirable topossibly minimize the size of the optical path tube 3. In principle,even if a carbon tube having a diameter of about several nanometers(nm=10⁻⁹ m) is used as the optical path tube 3, the variation in theluminance can be sensed by the CCD camera 7 to measure the temperature.

Although a quartz glass is generally used as the material of the windowsection 13, sapphire is used in the embodiment. As a result ofinventor's research of the present invention, it has been confirmed thatthe transmittance of light in an infrared range used for the temperaturemeasurement can be increased by using sapphire. Use of sapphire in thewindow section 13 is efficient to measure temperature with a temperatureresolution of 1° C. or less in a high-temperature range exceeding 1420°C.

For the comparison and the verification of the results of themeasurement by the temperature measuring apparatus according to thepresent invention as described above, an experiment is conducted in anarrangement in which a thermocouple 11 including platinum and aplatinum-rhodium alloy is disposed in the apparatus of FIG. 1, thethermocouple being in contact with the molten silicon 1 as shown in FIG.2. That is, since the temperature of the molten silicon 1 can berelatively correctly measured by using the thermocouple 11, the validityof the results of the measurement by the temperature measuring apparatusof the present invention can be evaluated by making a check to determinewhether or not the results match those of this measurement by thethermocouple 11. Incidentally, the thermocouple 11 as above lowerspurity of the molten silicon 1 when the thermocouple 11 is mounted.Therefore, the thermocouple 11 is not suitable for practical uses. Asignal of temperature measured by the thermocouple 11 is inputted via adigital multimeter 12 to the computer 10.

FIGS. 3 to 5 show the results of the temperature measurement oftemperature by the above apparatus in which a silicon floating zonehaving a height of 10 mm and a diameter of 10 mm is generated to measurethe temperature of the molten silicon 1. FIG. 3 is a graph in which asolid line indicates variation in the temperature measured by thethermocouple (thermocouple method) and dots represent variation intemperature measured by the temperature measuring apparatus according tothe present invention (non-contact method). In this regard, variation inluminance of the results measured in the non-contact method isrepresented using the ordinate on the right side. FIGS. 4 and 5 aregraphs showing Fourier spectra of temperature variation during 102.4seconds shown in FIG. 3. FIG. 4 is a Fourier spectrum of temperaturevariation in the results measured in the non-contact method according tothe present invention and FIG. 5 shows a Fourier spectrum of temperaturevariation in the results measured in the thermocouple method.

It is clearly seen from FIG. 3 that the measured results of thenon-contact method according to the present invention satisfactorilymatch those of the thermocouple method. Furthermore, by comparing FIG. 4with FIG. 5, it is understood that the peaks of the respective graphssatisfactorily match each other. Particularly, the position of the peak,which corresponds to a main characterization of temperature variation,appears on a higher frequency side and is a position of about 0.14 Hz inboth graphs. It is appreciated from this event that the non-contacttemperature measuring apparatus according to the present invention canmeasure the variation in temperature of the molten silicon in thefloating zone with high precision.

INDUSTRIAL APPLICABILITY

As described above, the temperature measuring apparatus of the presentinvention is a relatively simple apparatus configured by adding anoptical path tube to the ordinary non-contact temperature measuringapparatus in which by extracting by the optical path tube only the lightpropagating from the molten silicon in a particular direction, lightradiated from the molten silicon can be extracted while reducing theinfluence of disturbance of light from various directions to therebymeasure the temperature of the molten silicon with high precision.

The temperature measuring apparatus of the present invention can besuitably used particularly to measure the temperature of the moltensilicon in a furnace growing a single crystal using the FZ method andcan also be suitably used to measure the temperature in an infraredannealing furnace, an infrared epitaxial furnace, or the like in which aheating process is conducted using high-luminance light.

1. A temperature measuring method of measuring temperature of a heatedsubstance in a furnace in which crystals are grown using a floating zonemethod including a high-luminance light source as a heating source,comprising the steps of: illuminating said heated substance with a highluminance light source comprising a halogen lamp having a peakwavelength of about 1 micrometer; introducing light to a temperaturemeasuring apparatus from the heated substance via an optical path tubemade of carbon and extending to the heated substance said optical pathtube extending substantially horizontally of said heated substance,measuring luminance of the light introduced via the optical path tubeusing an image receiver comprising a CCD camera, filtering lightentering the CCD camera with a wave length cut filter to interrupt lightin a predetermined wavelength range from about 1.0 to about 15.0micrometers; further filtering light entering the CCD camera with aband-pass filter to extract substantially all light in a predeterminedwavelength range from about 0.7 to about 1.1 micrometers; andcalculating temperature of the heated substance according to theluminance.
 2. A temperature measuring apparatus for non-contacttemperature measurement of a heated substance in a furnace in which acrystal is grown using a floating-zone method by measuring luminance ofa light radiated from the heated substance to obtain the temperature,said furnace using a high luminance light source comprising a halogenlamp having a peak wavelength of about 1 micrometer for heating saidsubstance and said substance generating said light as a result of saidheating, said temperature measuring apparatus comprising: a windowsection to transmit the light from the furnace to an external space, anoptical path tube made of carbon and extending from the window sectionto the heated substance said tube having a distal end positionedlaterally adjacent said heated substance and extends substantiallyhorizontally to said window section, an image receiver to receive thelight introduced from the heated substance via the optical path tube tothe window section and the external space; and a measurement device formeasuring the luminance of said received light as a measure of thetemperature; wherein: the image receiver comprises a CCD camera; theimage receiver includes a wave length cut filter to interrupt light in apredetermined wavelength range from about 1.0 to about 15.0 micrometers;and the image receiver includes a band-pass filter to extractsubstantially all light in a predetermined wavelength range from about0.7 to about 1.1 micrometers.
 3. A temperature measuring apparatusaccording to claim 2, wherein the heated substance is molten silicon. 4.A temperature measuring apparatus according to claim 2, wherein thewindow section is made of quartz.
 5. A temperature measuring apparatusaccording to claim 2, wherein the window section is made of sapphire.